1. Field of the Invention
The present invention relates to a device for detecting abnormality in a secondary battery, and more specifically, to a technology of detecting a looseness in a fastening member that fastens a connecting plate for connecting battery cells and a cell terminal together.
2. Description of the Related Art
A conventional lithium ion battery installed in an electric vehicle has a configuration in which battery modules made up of a plurality of battery cells are connected together in parallel or series, and is designed to supply electric power to the vehicle.
In order to connect a plurality of battery cells in this manner, it is common to connect the terminals of the battery cells together by fastening the terminals to an electrically-conductive connecting plate such as a bus bar with fastening members.
The foregoing configuration, however, has the problem that the fastening members that fasten the connecting plate and the terminals together become loose once in a while due to vibration or the like. Such looseness in the fastening members increases contact resistance between the terminals and the connecting plate, and incurs energy loss.
A well-known way to avoid such a problem is to attach a pressure sensor to each fastening member and detect looseness in fastening members (see Unexamined Japanese Patent Publication No. 9-306468).
An electric vehicle is equipped with a number of battery modules, and accordingly, many fastening members are utilized. A battery pack formed by connecting a plurality of battery cells likewise uses a lot of fastening members.
Since the fastening members have their respective pressure sensors, the conventional technology disclosed in the above-mentioned patent document 1 involves a large number of pressure sensors, and accordingly requires high parts cost. On top of that, the battery pack inevitably contains a lot of wires. This deteriorates maintainability and is therefore undesirable.